For the first time ever, scientists have discovered a pair of
supermassive black holes in the same galaxy. The team of Professor
Guenther Hasinger and Dr. Stefanie Komossa from the Max Planck Institute
for Extraterrestrial Physics in Garching near Munich made the discovery
using NASA's Chandra X-ray Observatory. The black holes in the nucleus of
the galaxy NGC 6240 will merge in several hundred million
years from now creating an even larger black hole. A burst of
gravitational waves will accompany this merging.
The extraordinarily bright galaxy NGC 6240 is
roughly 400 million light years away from earth and is a prime example of
the collision and subsequent merging of two galaxies causing "fireworks"
as new stars are created. The center of this galaxy is hidden behind
innumerable dusty gas clouds and is therefore not visible with optical
telescopes. X-rays can, however, penetrate the veil of gas
and dust.
Previous observations have shown that NGC 6240
produces high energy X-radiation. Using radio, infrared, and optical
observations, astronomers detected two bright nuclei in this system, whose
nature remained a mystery. "With Chandra, we hoped to determine which of
the two nuclei, if any, contains an active super massive black hole," says
Stefanie Komossa from the Max Planck Institute for Extraterrestrial
Physics and lead author of the paper on NGC 6240 that is soon
to be published in the Astrophysical Journal
Letters. NASA's Chandra observed NGC 6240 with the
Advanced CCD Imaging Spectrometer
(ACIS) for a total of 10.3 hours.
"Much to our surprise, we found that both nuclei harbor active
black holes", explains Komossa. The detection of a binary black hole
supports the idea that black holes can grow to become enormously massive
in the centers of galaxies by merging with other black holes. "This is
important for our understanding of how galaxies form and evolve."
"The breakthrough came with Chandra's ability to clearly
distinguish the two nuclei and measure the details of the
X-radiation from each nucleus," says Guenther Hasinger,
director at the Max Planck Institute for Extraterrestrial Physics and
co-author of the paper. According to Hasinger, both active cosmic monsters
leave fingerprints. "We have observed an excess of high energy photons
from hot gas swirling around a black hole and X-rays from
fluorescing iron atoms in gas near the black hole."
Figure 1: X-ray zoom into the
nucleus of the nearby, ultra luminous galaxy NGC 6240 using
X-rays reveals two black holes. The conspicuous of galaxy NGC
6240 as seen on the left from a telescope on earth are remnants of
a collision between two galaxies that are now gradually merging with each
other. Thick dust and gas clouds hide the galaxy's nucleus, which cannot
be observed in visible light. X-rays can, however, penetrate this curtain.
On the right, Chandra imaged two extremely massive black holes that betray
themselves by high energy radiation (black rings). The figures are
color-coded. Regions with low radiation are red, and those with high
energy radiation are blue.
Images: Max Planck Institute for Extraterrestrial Physics
(optical image from W. Keel)
Over the next few hundred million years, the two black holes
in NGC 6240, which are roughly 3000 light years apart, will
drift toward each other and eventually merge to form an even larger,
supermassive black hole. The process will end several hundred million
years from now with an enormous burst of gravitational waves. These
gravitational waves will spread through the universe and produce ripples
in the fabric of space, which will appear as minute changes in the
distance between any two points.
The merging of two super massive black holes like those in
NGC 6240 will create the most powerful gravitational waves in
the universe. LISA (Laser Interferometer Space
Antenna), the space-based detector planned by NASA and
ESA, will search for gravitational waves from massive black
hole mergers. Such events are estimated to occur several times each year
in the observable universe. "This is the first time that we see a binary
black hole in action, the smoking gun evidence for something which will
become a major gravitational wave burst in the future", says Hasinger.
Figure 2: High energy
radiation (blue) emanating from the two black holes in the center of the
galaxy NGC 6240 superimposed with an optical image from the
Hubble Space Telescope (yellow).
Image: NASA / Max Planck Institute for Extraterrestrial
Physics
Figure 3: In addition to the
high energy radiation emanating from the center of NGC 6240,
there are also regions of lower energy, which are depicted in red.
Superimposed on this is a picture from the Hubble Space Telescope (yellow
and blue). The low-energy X-radiation does not come from the two black
holes but is attributed to the afterglow of earlier supernovae in the
center of the galaxy. They point to a "firework" of supernovae, which
catapulted their outer layers into space. If these stellar winds collide
with the surrounding interstellar medium, the gas heats up and glows in
the X-ray band.
Image: NASA / Max Planck Institute for Extraterrestrial
Physics
Other members of the team include Vadim Burwitz and Peter
Predehl from the Max Planck Institute for Extraterrestrial Physics, Jelle
Kaastra from the Space Research Organization in the Netherlands, and
Yasushi Ikebe from the University of Maryland in Baltimore.
NASA's Marshall Space Flight Center in Huntsville, Alabama
manages the Chandra program for the Office of Space Science in Washington.
The company TRW in Redondo Beach, California is the prime contractor for
the spacecraft. The Smithsonian's Chandra X-ray Center controls science
and flight operations from Cambridge, Massachusetts. The Deutsches Zentrum
fuer Luft- und Raumfahrt (DLR) funded Germany's contribution to
Chandra.
Images and additional information are available online at:
http://chandra.harvard.edu/, http://chandra.nasa.gov/, http://www.mpe.mpg.de/
PDF-Version... (0,8 MB)
Contact:
Prof. Guenther Hasinger
Max Planck Institute for Extraterrestrial
Physics
Giessenbachstraße
85748 Garching
Phone: +49-89 - 30000 -
3402
Fax: +49-89 - 30000 - 3569
E-Mail: ghasinger@mpe.mpg.de
Dr. Stefanie Komossa
Max Planck Institute for Extraterrestrial
Physics
Giessenbachstraße
85748 Garching
Phone: +49-89 - 30000 -
3577
Fax: +49-89 - 30000 - 3569
E-Mail: skomossa@mpe.mpg.de
